This invention is related to regulating the temperature of a substrate utilized in vapour deposition, in particular, in chemical vapour deposition.
Chemical and physical vapour deposition processes developed in the last few decades can produce high purity substances in commercial quantities. One of the more significant of such processes is, for example, the production of diamonds, usually in the polycrystalline state, utilizing a plasma source. The production of diamonds by vapour deposition is accompanied by high thermal energy transfer. Should the heat transfer and substrate temperature regulation be inadequate, the crystallization and rate of growth of the deposit obtained, in particular, the uniform quality of the deposited diamond cannot be maintained. In other words, the temperature regulation and control of the substrate is a critical feature in both a physical or a chemical vapour deposition (CVD) process. A frequently implemented method of substrate temperature control is regulating the heat loss of the substrate support or substrate mount means. Regulated heat loss of the substrate support or substrate mount is usually effected by conducting heat away in a controlled manner by some medium in contact with the substrate mount, as well as by regulating the heat removed by a heat sink. In U.S. Pat. No. 5,527,392, issued to Snail et al. on Jun. 28, 1996, a device for controlling the temperature of the substrate mount in a CVD reactor is described. A mixture of gases having such composition as to yield a desired mean thermal conductivity, is fed to the device, to flow at known flow rates about and around the substrate mount located in a housing. In addition, the geometry and the material of which the substrate mount is made of, are selected to provide further control of the heat transfer capability of the substrate mount. The housing acts as the heat sink, and has means for a cooling fluid as well. One of the difficulties with the above arrangement is that large and cumbersome gas tanks need to be installed to provide steady and reliable gas flows, as the heat control system is very sensitive to changes in the gas composition.
The metallurgical industries have been using sand or similar inert particles and air circulating between the particles in a vat or in a pile, for surrounding a large metal body which has been previously heated to a very high temperature, or for encasing a casting, to provide a particulate medium for controlled or slow cooling of the metal body or cast. There are known heat transfer methods utilizing multi-phase systems in other industries. For example, U.S. Pat. NO. 5,170,930, issued to T. P. Dolbear et al. on Dec. 15, 1992, describes a liquid metal paste for utilization in fast cooling of electronic components and solid state chips. The semi-solid paste is made up of low melting metals and alloys, and solid particles of higher melting point materials, or in some instances, ceramic particles. The paste is required to have high viscosity, be both electrically and thermally conductive at temperatures close to room temperature, and have additional characteristics specified useful in the electronics industry. It is noted that the primary function of the metal paste is to conduct heat away fast, and not to regulate the temperature of the electronic component at a certain level. Another multi-phase composition for fast cooling is described in U.S. Pat. NO. 5,604,037, issued to J. -M. Ting et al. on Feb. 18, 1997. The multi-phase composition comprises a diamond/carbon/carbon fibre composite coated with a metallic layer for use as a dielectric heat sink in electronic systems.
In the above multi-phased cooling devices utilized by the electronics and metallurgical industries heat is removed, but no importance is attached to maintaining the temperature of the system under consideration at a prerequisite level. There is a need for regulating the temperature of a substrate or the surface temperature of a substrate engaged in an exothermic reaction yielding a deposit, by regulating the heat loss by means of controlled heat transfer.
A heat transfer regulating mixture having a metallic component A with a melting point TA and a particulate ceramic component B which is non-wettable by the metallic component A, non-reactive therewith and which has a melting temperature TB which is higher than both the temperature TA and a desired operating temperature TD which is also higher than TA . The metallic component A and the particulate ceramic component B and the respective amounts will typically be selected to have a lower thermal resistivity above TA than below TA .
The metallic component A may be aluminum, tin, lead, gallium, indium, copper, silver and alloys thereof.
The particulate ceramic component B may be of alumina, titanium nitride, titanium carbide, titanium carbonitride, boron nitride, boron carbide, silicon carbide, silica and mixtures thereof.
The particulate component B may have an average particle size from 1 xcexcm to 150 xcexcm.
The heat transfer regulating mixture may be incorporated in the heat transfer regulating device having the mixture within an enclosure having first and second contact faces.
The heat transfer regulating device may be a cooking vessel, a shield wall, tube furnace or part of a substrate holder assembly for supporting a substrate body during a vapour deposition process.